We thank the authors for their interest in our work. We agree on many fundamental points, including the importance of the percent tissue altered (PTA) at the time of laser in situ keratomileusis (LASIK) and that multiple screening parameters must be utilized. We propose the PTA as a robust metric in patients without topographic abnormalities, historically the most difficult patients to identify and exclude from LASIK. We do not propose that PTA is the only important metric and hope that is clear to all readers.
The authors stated their opinion on Placido topography capability on detecting subclinical keratoconus. In contrast, a recent study by Bae and associates evaluated nearly every parameter generated by the Pentacam device in comparative populations of unilateral keratoconus and normal populations and found that the most robust differentiating metrics were anterior curvature and topometric indices, while no thickness variables were able to distinguish fellow keratoconus eyes from normal eyes. Thus, there remains disagreement in the published literature about which Scheimpflug-based metrics are most robust for screening.
Another important point is that the “fellow eye” of a frank keratoconus eye used routinely to investigate subclinical keratoconus should not be compared to the situation where we have both eyes with normal topography pattern, as we defined in our study, for obvious reasons. We provided scientific evidence of the association of a high PTA and ectasia in the normal population. The purpose was not to identify subclinical forms of keratoconus.
We agree that Scheimpflug provides more thickness data than central thickness alone and that central thickness can overestimate the thinnest point. However, the overall importance of this for patients without topographic abnormalities will hopefully be better elucidated in future studies. In their recent study, Ambrosio and associates did not discuss any significant differences between central and thinnest pachymetry and used central thickness values for modeling even though they had both measurements available.
We are aware of potential differences between flap thickness and ablation owing to flap architecture. It has been addressed recently by one of us. However, we are uncertain of the significance, given the reality of ablation always occurring with flap creation for LASIK and a minimal ability to modify flap architecture much beyond current approaches.
The authors’ data are not fully comparable to ours because of inaccuracy in the flap thickness value. The PTA was derived from estimated flap thickness values and not from real flap thickness measurement, which was an inclusion criterion for our study. This is crucial at this stage of the investigation in order to determine the specific PTA value where ectasia occurred.
We have consistently stated that multiple metrics must be evaluated for thorough LASIK screening, including patient age. We feel the combination of PTA, age, topography, and, potentially, other factors may yield important advances in screening algorithms.
Finally, this paper brings enough scientific evidence that PTA should be incorporated into clinical practice, taken into account when screening patients for LASIK and considered together with previous validated risk factors.